A novel high-sensitive upconversion thermometry strategy: Utilizing synergistic effect of dual-wavelength lasers excitation to manipulate electron thermal distribution

Conventional upconversion thermometry strategy, based on the thermally coupled levels (TCL) of lanthanide ions, confronts a dilemma in simultaneously achieving high absolute/relative temperature ( T ) sensitivities ( S a and S r ) and good signal discriminability. Herein, a novel thermometry strategy by utilizing the synergistic effect of dual-wavelength lasers to manipulate electron thermal distribution is proposed to go beyond the limitation of the TCL-based strategy. In the case of NaGdF 4 : 20%Yb 3+ , 2%Er 3+ nanoparticles upon 980 & 1530 nm dual-excitation, it is found that more efficient utilization of excited photons results in a higher electron concentration in ladder-like energy levels of Er 3+ , owing to the diverse pumping routes, which increases transition rate of the T -dependent phonon-assisted cross-relaxation process, and in turn establishes a thermally-sensitive electronic connection between Er 3+ : 2 H 11/2 , 4 S 3/2 and Er 3+ : 4 F 9/2 . Remarkably, not only a highest record value of S a (0.0365 K −1 ) for the Er 3+ doped host materials in the physiological temperature range (303–343 K) is achieved, but also a high S r (1.29% K -1 ) and an excellent signal discriminability (Δλ = 112 nm) are obtained. Combining a much intensified upconversion (UC) signal and a good size/shape homogeneity in nanometer scale, the investigated NaGdF 4 : 20%Yb 3+ , 2%Er 3+ upon dual-wavelength excitation is potentially applicable in the intracellular thermal sensing and imaging. This work exploits an effective way to develop high-performance T -sensors, and the proposed thermometry strategy can be extended to surges of the other lanthanide ions doped systems pumped by multiple-wavelength lasers.